A single cycle of treatment with temozolomide, alone or combined with O6-benzylguanine, induces strong chemoresistance in melanoma cell clones in vitro: Role of O6-methylguanine-DNA methyltransferase and the mismatch repair system

Ester Alvino, Daniele Castiglia, Simona Caporali, Rita Pepponi, Patrizia Caporaso, Pedro Miguel Lacal, Giancarlo Marra, Franziska Fischer, Giovanna Zambruno, Enzo Bonmassar, Joseph Jiricny, Stefania D'Atri

Research output: Contribution to journalArticle

Abstract

Clinically achievable concentrations of temozolomide (TMZ) produce cytotoxic effects only in mismatch repair (MMR)-proficient cells endowed with low O6-methylguanine-DNA methyltransferase (MGMT) activity. Aim of the present study was to investigate the molecular mechanisms underlying acquired resistance of melanoma cells to TMZ and the effect of O 6-benzylguanine (BG), a specific MGMT inhibitor, on the development of a TMZ-resistant phenotype. Three MMR-proficient melanoma cell clones with low or no MGMT activity were treated daily for 5 days with 50 μmol/l TMZ, alone or in combination with 5 μmol/l BG. Parental clones and sublines established after one or four cycles of treatment were analyzed for sensitivity to TMZ or TMZ+BG and for other parameters. The sublines established after one cycle of TMZ or TMZ+BG exhibited a marked increase in MGMT activity and resistance to TMZ alone. BG only partially reversed acquired resistance to the drug. In some cases, alterations in the MMR system accounted for MGMT-independent resistance to TMZ. Up-regulation of MGMT activity was associated with either demethylation of the MGMT promoter or hypermethylation of the body of the gene, and partially reversed by 5-aza-2′-deoxycytidine. The sublines established after four cycles of TMZ or TMZ+BG did not show a further increase in resistance to TMZ alone. However, two out of three sublines established after TMZ+BG treatment exhibited increased resistance to TMZ+BG. In conclusion, our data demonstrate that a single cycle of TMZ is sufficient to induce high levels of drug resistance in melanoma clones, principally, but not exclusively, via up-regulation of MGMT expression. Exposure to TMZ+BG favors the development of MGMT-independent mechanisms of TMZ resistance.

Original languageEnglish
Pages (from-to)785-797
Number of pages13
JournalInternational Journal of Oncology
Volume29
Issue number4
Publication statusPublished - Oct 2006

Keywords

  • Chemoresistance
  • Melanoma
  • Mismatch repair
  • O-methylguanine-DNA methyltransferase
  • Temozolomide

ASJC Scopus subject areas

  • Cancer Research
  • Oncology

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